In IEEE 802.11 WLANs, an access point (AP) or a station (STA) use management frames to conduct certain management functions. Examples of the management frames are Association Request, Association Response, Reassociation Request, Reassociation Response, Probe Request and Probe Response frames.
The IEEE 802.11e extends the IEEE 802.11 standards with new management frames. Some of those new management frames are called action frames. The action frames are used for conducting certain functions such as quality of service (QoS) traffic stream set-up, direct link set-up, block acknowledgment (ACK) set-up, or the like. Examples of the action frames include Add Traffic Stream (ADDTS) Request, ADDTS Response, Direct Link Setup (DLS) Request, DLS Response, Add Block acknowledgement (ACK) (ADDBA) Request, Add Block ACK Response, Delete Block ACK (DELBA) Request, or the like.
Currently, the IEEE 802.11n extension has been proposed for achieving higher throughput (HT). In the IEEE 802.11n proposal, new action frames are introduced for providing transmission mode and channel information feedback. Transmission mode feedback allows a receiving station to inform a transmitting station of the preferred mode for the current channel conditions. The particular choice of mode is determined by the receiving station. The transmitting station may or may not use the particular mode, depending on its capabilities. A receiving station may also decline to provide a preferred mode. Channel information feedback provides a mechanism for a transmitting station to learn the precise channel seen at the receiving station. This information may either be used as part of a calibration, for systems that assume channel reciprocity, or as direct channel feedback. A receiving station may either provide a complete channel estimate or a null response. Examples of the IEEE 802.11n action frames are Mode Request, Mode Response, multiple-input multiple-output (MIMO) Channel Request and MIMO Channel Response frames.
Management frames, (including action frames), may be broadcast or multicast to multiple responders, (e.g., via a beacon frame), or alternatively may be unicast to a specific (single) responder, (e.g., ADDBA Request, ADDBA Response, Mode Request, Mode Response, MIMO Channel Request and MIMO Channel Response). When a management or action frame is unicast to a specific responder, the IEEE 802.11 standard requires the responder to acknowledge the receipt of such frame by sending an ACK packet. On the other hand, if the management or action frame is broadcast or multicast to multiple responders, the IEEE 802.11 standard does not require the responders to acknowledge the receipt of such frame.
FIG. 1 is a signaling diagram of a prior art process 100 for exchanging management or action frames between an initiator 102 and a responder 104. The initiator 102 accesses the wireless medium, which needs some delay corresponding to the contention or access delay under the IEEE 802.11 standards, and sends an action frame, (e.g., a Mode Request frame), to the responder 104 (step 112). Upon correctly receiving the action frame, the responder 104 access the wireless medium, which also needs some delay, (e.g., a delay corresponding to a short inter-frame spacing (SIFS)), and sends an ACK packet to the initiator 102 (step 114). The responder 104 then prepares an action frame, (e.g., a Mode Response frame), including the data requested by the initiator 102 and then accesses the wireless medium again, which needs some delay due to contention or access delay, and sends the action frame to the initiator 102 (step 116). This time, the delay may be substantially long because it is possible that other stations may exchange packet at that time and therefore the responder 104 may not be able to access the medium as it wants to. Upon correctly receiving the action frame from the responder 104, the initiator 102 accesses the wireless medium, which also needs some delay, (typically a time period corresponding to the SIFS), and sends an ACK packet to the responder 104 (step 118).
In the prior art process 100, since the responder 104 has to first send an ACK packet (step 114) and then has to incur a contention or access delay in order to access the wireless medium to send the response frame at step 116, the responsiveness for exchanging such management or action frames is relatively slow. Such slow management or action frame response may degrade the performance of the WLAN since the information may not be valid or relevant at the time it is delivered. For example, since transmission mode feedback allows the responder 104 to specify or indicate to the initiator transmission-related information including a data rate, a modulation and coding scheme (MCS), the number of spatial streams in MIMO and the guard interval, such information should be exchanged as quickly as possible. However, under the prior art scheme, the exchange of such information may be substantially delayed.
Therefore, a new mechanism to exchange the management or action frames in a very short period of time is desirable.